1. Field of the Invention
This invention relates to a high-speed sputtering apparatus using a target of ferromagnetic substance, such as Fe, Co, Fe--Ni, Co--Cr, Co--R, Fe.sub.3 O.sub.4, BaO.Fe.sub.2 O.sub.3 or the like.
2. Description of the Prior Art
Sputtering apparatuses are known which use a target of a ferromagnetic substance as a cathode in which the cathode and a substrate are positioned in the evacuable treatment chamber. The target of ferromagnetic substance comprises at least two separate segments of ferromagnetic substance which are spaced apart, one from another, by a small gap so that a magnetic field from a magnetic field generating means positioned behind the target is leaked out to the surface of the target of ferromagnetic substance. Japanese Patent Application Nos. Sho-56-44132 and Sho 56-44133 illustrate this type of prior art apparatus.
This type of prior art apparatus has the advantage that even if the intensity of the magnetic field generated by the magnetic field generating means is below the magnetic saturation value of the ferromagnetic substance, there is a comparatively large leakage magnetic field on the surface of the target and the target of the ferromagnetic substance can thus be made with a relatively large thickness--with the result that sputtering of the ferromagnetic substance can be carried out for a long time and at a high efficiency. If, in this type of apparatus, the small gap between the adjacent segments of ferromagnetic substance is below about 3 mm, the plasma does not enter the gap under ordinary electric discharge conditions and thus there is no possibility of sputtering of the backing plate provided on the back of the target of ferromagnetic substance.
However, it has been found that there is a possibility of an unfavorable phenomenon in that the backing plate is sputtered and the resultant particles adhere as foreign matter to the substrate, even though the plasma does not enter the small gap of 3 mm or so under certain conditions of varied electric discharge conditions. The cause of this phenomenon is not clear but it appears that ions of a gas such as Ar or the like, charged in the vacuum treatment chamber, are accelerated in speed at a dark space formed between the target and a plasma region ahead of the target and some of them pass through the small gap and sputter the backing plate.